1. Field of the Invention
This invention relates to apparatus for displaying an image suspended in space, comprising: an object for display; a retroreflector being arranged to receive light from the object; a beamsplitter in a path for light from the object to the retroreflector, the beamsplitter being arranged at an oblique angle to the direction of propagation of the light such that it transmits part of the light and reflects part of the light, the light being either transmitted or reflected by the beamsplitter is received by the retroreflector and is reflected by it back to the beamsplitter, which either reflects or transmits part of this retroreflected light to form a real image suspended in space.
2. Background
A known display apparatus of this type is described in EP-A-0460873.
According to a first aspect of the present invention there is provided apparatus as defined in the first paragraph above, characterized in that the apparatus further comprises a concave mirror being arranged between the beamsplitter and the retroreflector such that light from the beamsplitter is reflected by the concave mirror to the retroreflector which reflects it back via the concave mirror towards the beamsplitter in use. The presence of a concave mirror between the beamsplitter and the retroreflector can improve viewability of the image by avoidance of reflections from the surfaces of one or more converging lenses.